1. Field of the Invention
The present invention relates to circuit boards and more particularly, to an EMI-resistant circuit board assembly, which prevents the characteristics of devices and circuits from interference by the electromagnetic wave of high-frequency noises.
2. Description of the Related Art
The arrangement of electronic devices on a circuit board must be determined subject to the function of the electronic circuit and must consider electric coupling or electromagnetic interference among devices. For example, the high-speed digital processor or control switch of an electronic circuit or the antenna of a high-frequency circuit produces high-frequency electromagnetic waves under a high speed or high frequency operation environment. The high-frequency noises will more or less interfere with the transmission of analogue audio or video signal, thereby affecting signal transmission performance. Therefore, the circuit layout of a circuit board must consider the function of electromagnetic interference (EMI) resistance.
FIGS. 1 and 2 illustrate an EMI-resistant circuit board 1 according to the prior art. According to this design, the EMI-resistant circuit board 1 comprises a plurality of high-frequency circuit regions 11. Each high-frequency circuit region 11 is comprised of a plurality of electronic devices 110 that produce high-frequency noises during operation, and a plurality of metal frames 111 that surround the effective circuit of each of the electronic devices 110 and separate the electronic device 110 from one another. As shown in FIG. 2, a plurality of metal shielding masks 12 are respectively covered on the high-frequency circuit regions 11 and disposed in contact with the metal frames 111 to guide high-frequency noises to the ground potential. Therefore, the high-frequency noises produced in the high-frequency circuit regions 11 are shielded without affecting the electric properties of other devices and circuits, and the metal frames 111 prevent electromagnetic interference among the high-frequency electronic devices 110. However, because the metal shielding masks 12 are respectively configured subject to the configuration of the high-frequency circuit regions 11, the fabrication of the metal shielding boards 12 is complicated and expensive. In case of employing the design to have the high-frequency circuit regions 11 be arranged together, only one single metal shielding mask 12 is necessary to shield the high-frequency circuit regions 11. However, if the borders of the high-frequency regions 11 do not match with one another, the design will waste much circuit space. In this case, the high-frequency regions 11 will occupy much surface area of the circuit board 1. In consequence, the size of final product will be relatively increased, and other circuit function designs must be relatively reduced, thereby degrading the integrity of circuit function of the electronic product.